Polysulfide stabilization by tyrosine and hydroxyphenyl-containing derivatives that is important for a reactive sulfur metabolomics analysis.

The physiological importance of reactive sulfur species (RSS) such as cysteine hydropersulfide (CysSSH) has been increasingly recognized in recent years. We have established a reactive sulfur metabolomics analysis by using RSS metabolic profiling, which revealed appreciable amounts of RSS generated endogenously and ubiquitously in both prokaryotic and eukaryotic organisms. The chemical nature of these polysulfides is not fully understood, however, because of their reactive or complicated redox-active properties. In our study here, we determined that tyrosine and a hydroxyphenyl-containing derivative, ß-(4-hydroxyphenyl)ethyl iodoacetamide (HPE-IAM), had potent stabilizing effects on diverse polysulfide residues formed in CysSSH-related low-molecular-weight species, e.g., glutathione polysulfides (oxidized glutathione trisulfide and oxidized glutathione tetrasulfide). The protective effect against degradation was likely caused by the inhibitory activity of hydroxyphenyl residues of tyrosine and HPE-IAM against alkaline hydrolysis of polysulfides. This hydrolysis occurred via heterolytic scission triggered by the hydroxyl anion acting on polysulfides that are cleaved into thiolates and sulfenic acids, with the hydrolysis being enhanced by alkylating reagents (e.g. IAM) and dimedone. Moreover, tyrosine prevented electrophilic degradation occurring in alkaline pH. The polysulfide stabilization induced by tyrosine or the hydroxyphenyl moiety of HPE-IAM will greatly improve our understanding of the chemical properties of polysulfides and may benefit the sulfur metabolomics analysis if it can be applied successfully to any kind of biological samples, including clinical specimens.

Persulfide synthases that are functionally coupled with translation mediate sulfur respiration in mammalian cells.

Cysteine persulfide and polysulfide are produced in cells and exist in abundance in both low MW and protein fractions. However, the mechanism of regulation of the formation of cellular cysteine polysulfides and the physiological functions of cysteine persulfides/polysulfides produced in cells are not fully understood. We recently demonstrated that cysteinyl-tRNA synthetase (CARS) is a novel cysteine persulfide synthase. CARS is involved in protein polysulfidation that is coupled with translation. In particular, mitochondria function in biogenesis and bioenergetics is also supported and up-regulated by cysteine persulfide derived from mitochondrial CARS (also known as CARS2). Here, we provide an overview of recent advances in reactive persulfide research and our understanding of the mechanisms underlying the formation and the physiological roles of reactive persufides, with a primary focus on the formation of cysteine persulfide by CARS and the most fundamental mitochondrial bioenergetics mediated by persulfides, that is, sulfur respiration. LINKED ARTICLES: This article is part of a themed section on Chemical Biology of Reactive Sulfur Species. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.4/issuetoc.

Production of 8-nitro-cGMP in osteocytic cells and its upregulation by parathyroid hormone and prostaglandin E2.

Osteocytes regulate bone remodeling, especially in response to mechanical loading and unloading of bone, with nitric oxide reported to play an important role in that process. In the present study, we found that 8-nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP), a second messenger of nitric oxide in various types of cells, was produced by osteocytes in bone tissue as well as cultured osteocytic Ocy454 cells. The amount of 8-nitro-cGMP in Ocy454 cells increased during incubation with parathyroid hormone or prostaglandin E2, both of which are known to upregulate receptor activator of nuclear factor-κB ligand (RANKL) mRNA expression in osteocytes. On the other hand, exogenous 8-nitro-cGMP did not have effects on either the presence or absence of these bioactive substances. Furthermore, neither an inhibitor of nitric oxide synthase nor 8-bromo-cGMP, a cell-permeable analog of cGMP, showed remarkable effects on mRNA expression of sclerostin or RANKL. These results indicate that neither nitric oxide nor its downstream compounds, including 8-nitro-cGMP, alone are sufficient for induction of functional changes in osteocytes.

Reactive Persulfides from Salmonella Typhimurium Downregulate Autophagy-Mediated Innate Immunity in Macrophages by Inhibiting Electrophilic Signaling.

Reactive persulfides such as cysteine persulfide and glutathione persulfide are produced by bacteria including Salmonella during sulfur metabolism. The biological significance of bacterial reactive persulfides in host-pathogen interactions still warrants investigation. We found that reactive persulfides produced by Salmonella Typhimurium LT2 regulate macrophage autophagy via metabolizing 8-nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP), an electrophilic product of reactive oxygen species and nitric oxide signaling. 8-Nitro-cGMP signaling was required for efficient autophagy-mediated clearance of Salmonella from infected macrophages. In the infected cells, 8-nitro-cGMP caused cGMP adduct formation (S-guanylation) of bacterial surface proteins, which triggered recruitment of autophagy-related proteins p62 and LC3-II to the intracellular bacteria. We also found that Salmonella-produced reactive persulfides downregulated this autophagy by decreasing cellular 8-nitro-cGMP content, thereby inhibiting electrophilic signaling. These data reveal a pathogenic role of bacteria-derived reactive persulfides via suppression of anti-bacterial autophagy.

Important Role of Endothelial Caveolin-1 in the Protective Role of Endothelium-dependent Hyperpolarization Against Nitric Oxide-Mediated Nitrative Stress in Microcirculation in Mice.

AIMS: Nitric oxide (NO) and endothelium-dependent hyperpolarization (EDH) play important roles in maintaining cardiovascular homeostasis. We have previously demonstrated that endothelial NO synthase (eNOS) plays diverse roles depending on vessel size, as a NO generating system in conduit arteries and an EDH-mediated system in resistance arteries, for which caveolin-1 (Cav-1) is involved. However, the physiological role of endothelial Cav-1 in microvessels remains to be elucidated. METHODS AND RESULTS: We newly generated endothelium-specific Cav-1-knockout (eCav-1-KO) mice. eCav-1-KO mice showed loss of endothelial Cav-1/eNOS complex and had cardiac hypertrophy despite normal blood pressure. In eCav-1-KO mice, as compared to wild-type controls, the extent of eNOS phosphorylation at inhibitory Thr495 was significantly reduced in mesenteric arteries and the heart. Isometric tension and Langendorff-perfused heart experiments showed that NO-mediated responses were enhanced, whereas EDH-mediated responses were reduced in coronary microcirculation in eCav-1-KO mice. Immunohistochemistry showed increased level of 8-nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP), a marker of nitrative stress, in the heart from eCav-1-KO mice. S-guanylation of cardiac H-Ras in eCav-1-KO mice was also significantly increased compared with wild-type controls. CONCLUSIONS: These results suggest that eCav-1 is involved in the protective role of EDH against nitrative stress caused by excessive NO to maintain cardiac microvascular homeostasis.

Cysteinyl-tRNA synthetase governs cysteine polysulfidation and mitochondrial bioenergetics.

Cysteine hydropersulfide (CysSSH) occurs in abundant quantities in various organisms, yet little is known about its biosynthesis and physiological functions. Extensive persulfide formation is apparent in cysteine-containing proteins in Escherichia coli and mammalian cells and is believed to result from post-translational processes involving hydrogen sulfide-related chemistry. Here we demonstrate effective CysSSH synthesis from the substrate L-cysteine, a reaction catalyzed by prokaryotic and mammalian cysteinyl-tRNA synthetases (CARSs). Targeted disruption of the genes encoding mitochondrial CARSs in mice and human cells shows that CARSs have a crucial role in endogenous CysSSH production and suggests that these enzymes serve as the principal cysteine persulfide synthases in vivo. CARSs also catalyze co-translational cysteine polysulfidation and are involved in the regulation of mitochondrial biogenesis and bioenergetics. Investigating CARS-dependent persulfide production may thus clarify aberrant redox signaling in physiological and pathophysiological conditions, and suggest therapeutic targets based on oxidative stress and mitochondrial dysfunction.

Exposure to Electrophiles Impairs Reactive Persulfide-Dependent Redox Signaling in Neuronal Cells.

Electrophiles such as methylmercury (MeHg) affect cellular functions by covalent modification with endogenous thiols. Reactive persulfide species were recently reported to mediate antioxidant responses and redox signaling because of their strong nucleophilicity. In this study, we used MeHg as an environmental electrophile and found that exposure of cells to the exogenous electrophile elevated intracellular concentrations of the endogenous electrophilic molecule 8-nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP), accompanied by depletion of reactive persulfide species and 8-SH-cGMP which is a metabolite of 8-nitro-cGMP. Exposure to MeHg also induced S-guanylation and activation of H-Ras followed by injury to cerebellar granule neurons. The electrophile-induced activation of redox signaling and the consequent cell damage were attenuated by pretreatment with a reactive persulfide species donor. In conclusion, exogenous electrophiles such as MeHg with strong electrophilicity impair the redox signaling regulatory mechanism, particularly of intracellular reactive persulfide species and therefore lead to cellular pathogenesis. Our results suggest that reactive persulfide species may be potential therapeutic targets for attenuating cell injury by electrophiles.

Production of reactive persulfide species in chronic obstructive pulmonary disease.

BACKGROUND: Oxidative stress is a major aetiological factor driving chronic obstructive pulmonary disease (COPD). Recently recognised as potent antioxidants, reactive persulfide and polysulfide species are biosynthesised by cystathionine ß-synthase and cystathionine γ-lyase. The production of reactive persulfide and polysulfide species in the lungs of patients with COPD remain unknown. OBJECTIVES: The aim of this study was to examine the production of reactive persulfides and polysulfides, such as glutathione persulfide (GSSH), cysteine persulfide (CysSSH) and glutathione trisulfide (GSSSH), in lung-resident cells and epithelial lining fluid (ELF) obtained from patients with mild to moderate COPD. METHODS: Lung tissues, primary lung cells, ELF and sputum were obtained. The amounts of reactive persulfides and polysulfides in the cells and ELF were measured by liquid chromatography-tandem mass spectrometry with ß-(4-hydroxyphenyl) ethyl iodoacetamide as a trapping agent for hydroper/polysulfides. The amounts of synthases in the lung tissues, sputum and primary cells were quantified. RESULTS: The amounts of GSSH, CysSSH and GSSSH were decreased in the lung cells and ELF from patients with COPD. The amounts of reactive persulfides and polysulfides in the lung cells had a positive correlation with the degree of airflow limitation. By contrast, the amounts of the synthases were increased in the lung tissues and sputum cells of patients with COPD. CONCLUSIONS: We have identified a decrease in reactive persulfide and polysulfide species in the lungs of patients with COPD. These data suggest that the newly detected antioxidants reactive persulfides and polysulfides could be associated with the redox balance in the lungs of patients with COPD.

Metabolomic profiling of reactive persulfides and polysulfides in the aqueous and vitreous humors.

We investigate the metabolomic profile of reactive persulfides and polysulfides in the aqueous and vitreous humors. Eighteen eyes of 18 consecutive patients with diabetes mellitus (DM) and diabetic retinopathy underwent microincision vitrectomy combined with cataract surgery. Samples of the aqueous and vitreous humors were collected and underwent mass spectrometry-based metabolomic profiling of reactive persulfides and polysulfides (polysulfidomics). The effect of reactive polysulfide species on the viability of immortalized retinal cells (the RGC-5 cell line) under oxidative stress (induced with H2O2) was also evaluated with an Alamar Blue assay. The experiments showed that cysteine persulfides (CysSSH), oxidized glutathione trisulfide (GSSSG) and cystine were elevated in the aqueous humor, and CysSSH, Cys, and cystine were elevated in the vitreous. Furthermore, GSSSG, cystine, and CysSSH levels were correlated in the aqueous and vitreous humors. A comparison, in DM and control subjects, of plasma levels of reactive persulfides and polysulfides showed that they did not differ. In vitro findings revealed that reactive polysulfide species increased cell viability under oxidative stress. Thus, various reactive persulfides and polysulfides appear to be present in the eye, and some reactive sulfide species, which have a protective effect against oxidative stress, are upregulated in the aqueous and vitreous humors of DM eyes.

Protein polysulfidation-dependent persulfide dioxygenase activity of ethylmalonic encephalopathy protein 1.

Reactive persulfide species such as glutathione persulfide (GSSH) are highly abundant biomolecules. Persulfide dioxygenase (also called ethylmalonic encephalopathy protein 1, ETHE1) reportedly metabolizes GSSH to GSH with simultaneous oxygen consumption. How ETHE1 activity is regulated is still unclear, however. In this study, we describe the possible role of protein polysulfidation in the catalytic activity of ETHE1. We first found that ETHE1 catalyzed the persulfide dioxygenase reaction mostly for glutathione polysulfides, GS-(S)n-H, as well as for GSSH, but not for other endogenous persulfides such as cysteine and homocysteine persulfides/polysulfides. We then developed a novel method to detect protein polysulfidation and named it the polyethylene glycol-conjugated maleimide-labeling gel shift assay (PMSA). PMSA analysis indicated that most cysteine residues in ETHE1 were polysulfidated. Site-directed mutagenesis of cysteine residues in ETHE1 combined with liquid chromatography tandem mass spectrometry for polysulfidation determination surprisingly indicated that the Cys247 residue was important for polysulfidation of other Cys residues and that the C247S mutant possessed no persulfide dioxygenase activity. These results suggested that ETHE1 is a major enzyme regulating endogenous GSSH/GS-(S)n-H and that its activity is controlled by polysulfidation of the Cys247 residue.

Mice Deficient in Angiopoietin-like Protein 2 (Angptl2) Gene Show Increased Susceptibility to Bacterial Infection Due to Attenuated Macrophage Activity.

Macrophages play crucial roles in combatting infectious disease by promoting inflammation and phagocytosis. Angiopoietin-like protein 2 (ANGPTL2) is a secreted factor that induces tissue inflammation by attracting and activating macrophages to produce inflammatory cytokines in chronic inflammation-associated diseases such as obesity-associated metabolic syndrome, atherosclerosis, and rheumatoid arthritis. Here, we asked whether and how ANGPTL2 activates macrophages in the innate immune response. ANGPTL2 was predominantly expressed in proinflammatory mouse bone marrow-derived differentiated macrophages (GM-BMMs) following GM-CSF treatment relative to anti-inflammatory cells (M-BMMs) established by M-CSF treatment. Expression of the proinflammatory markers IL-1ß, IL-12p35, and IL-12p40 significantly decreased in GM-BMMs from Angptl2-deficient compared with wild-type (WT) mice, suggestive of attenuated proinflammatory activity. We also report that ANGPTL2 inflammatory signaling is transduced through integrin α5ß1 rather than through paired immunoglobulin-like receptor B. Interestingly, Angptl2-deficient mice were more susceptible to infection with Salmonella enterica serovar Typhimurium than were WT mice. Moreover, nitric oxide (NO) production by Angptl2-deficient GM-BMMs was significantly lower than in WT GM-BMMs. Collectively, our findings suggest that macrophage-derived ANGPTL2 promotes an innate immune response in those cells by enhancing proinflammatory activity and NO production required to fight infection.

Redox signaling regulated by an electrophilic cyclic nucleotide and reactive cysteine persulfides.

Reactive oxygen (oxidant) and free radical species are known to cause nonspecific damage of various biological molecules. The oxidant toxicology is developing an emerging concept of the physiological functions of reactive oxygen species in cell signaling regulation. Redox signaling is precisely modulated by endogenous electrophilic substances that are generated from reactive oxygen species during cellular oxidative stress responses. Among diverse electrophilic molecular species that are endogenously generated, 8-nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP) is a unique second messenger whose formation, signaling, and metabolism in cells was recently clarified. Most important, our current studies revealed that reactive cysteine persulfides that are formed abundantly in cells are critically involved in the metabolism of 8-nitro-cGMP. Modern redox biology involves frontiers of cell research and stem cell research; medical and clinical investigations of infections, cancer, metabolic syndrome, aging, and neurodegenerative diseases; and other fields. 8-Nitro-cGMP-mediated signaling and metabolism in cells may therefore be potential targets for drug development, which may lead to discovery of new therapeutic agents for many diseases.

Redox signaling regulated by electrophiles and reactive sulfur species.

Redox signaling is a key modulator of oxidative stress induced by nonspecific insults of biological molecules generated by reactive oxygen species. Current redox biology is revisiting the traditional concept of oxidative stress, such that toxic effects of reactive oxygen species are protected by diverse antioxidant systems upregulated by oxidative stress responses that are physiologically mediated by redox-dependent cell signaling pathways. Redox signaling is thus precisely regulated by endogenous electrophilic substances that are generated from reactive oxygen species and nitric oxide and its derivative reactive species during stress responses. Among electrophiles formed endogenously, 8-nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP) has unique cell signaling functions, and pathways for its biosynthesis, signaling mechanism, and metabolism in cells have been clarified. Reactive sulfur species such as cysteine hydropersulfides that are abundant in cells are likely involved in 8-nitro-cGMP metabolism. These new aspects of redox biology may stimulate innovative and multidisciplinary research in cell and stem cell biology; infectious diseases, cancer, metabolic syndrome, ageing, and neurodegenerative diseases; and other oxidative stress-related disorders. This review focuses on the most recent progress in the biosynthesis, cell signaling, and metabolism of 8-nitro-cGMP, which is a likely target for drug development and lead to discovery of novel therapeutics for many diseases.

Reactive cysteine persulfides and S-polythiolation regulate oxidative stress and redox signaling.

Using methodology developed herein, it is found that reactive persulfides and polysulfides are formed endogenously from both small molecule species and proteins in high amounts in mammalian cells and tissues. These reactive sulfur species were biosynthesized by two major sulfurtransferases: cystathionine ß-synthase and cystathionine γ-lyase. Quantitation of these species indicates that high concentrations of glutathione persulfide (perhydropersulfide >100 µM) and other cysteine persulfide and polysulfide derivatives in peptides/proteins were endogenously produced and maintained in the plasma, cells, and tissues of mammals (rodent and human). It is expected that persulfides are especially nucleophilic and reducing. This view was found to be the case, because they quickly react with H2O2 and a recently described biologically generated electrophile 8-nitroguanosine 3',5'-cyclic monophosphate. These results indicate that persulfides are potentially important signaling/effector species, and because H2S can be generated from persulfide degradation, much of the reported biological activity associated with H2S may actually be that of persulfides. That is, H2S may act primarily as a marker for the biologically active of persulfide species.

Promotion of atherosclerosis by Helicobacter cinaedi infection that involves macrophage-driven proinflammatory responses.

Helicobacter cinaedi is the most common enterohepatic Helicobacter species that causes bacteremia in humans, but its pathogenicity is unclear. Here, we investigated the possible association of H. cinaedi with atherosclerosis in vivo and in vitro. We found that H. cinaedi infection significantly enhanced atherosclerosis in hyperlipidaemic mice. Aortic root lesions in infected mice showed increased accumulation of neutrophils and F4/80(+) foam cells, which was due, at least partly, to bacteria-mediated increased expression of proinflammatory genes. Although infection was asymptomatic, detection of cytolethal distending toxin RNA of H. cinaedi indicated aorta infection. H. cinaedi infection altered expression of cholesterol receptors and transporters in cultured macrophages and caused foam cell formation. Also, infection induced differentiation of THP-1 monocytes. These data provide the first evidence of a pathogenic role of H. cinaedi in atherosclerosis in experimental models, thereby justifying additional investigations of the possible role of enterohepatic Helicobacter spp. in atherosclerosis and cardiovascular disease.

Endogenous nitrated nucleotide is a key mediator of autophagy and innate defense against bacteria.

Autophagy is a cellular self-catabolic process wherein organelles, macromolecules, and invading microbes are sequestered in autophagosomes that fuse with lysosomes. In this study, we uncover the role of nitric oxide (NO) as a signaling molecule for autophagy induction via its downstream mediator, 8-nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP). We found that 8-nitro-cGMP-induced autophagy is mediated by Lys63-linked polyubiquitination and that endogenous 8-nitro-cGMP promotes autophagic exclusion of invading group A Streptococcus (GAS) from cells. 8-nitro-cGMP can modify Cys residues by S-guanylation of proteins. We showed that intracellular GAS is modified with S-guanylation extensively in autophagosomes-like vacuoles, suggesting the role of S-guanylation as a marker for selective autophagic degradation. This finding is supported by the fact that S-guanylated bacteria were selectively marked with polyubiquitin, a known molecular tag for selective transport to autophagosomes. These results collectively indicate that 8-nitro-cGMP plays a crucial role in cytoprotection during bacterial infections or inflammations via autophagy upregulation.

Formation, signaling functions, and metabolisms of nitrated cyclic nucleotide.

8-Nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP) is a unique derivative of guanosine 3',5'-cyclic monophosphate (cGMP) formed in mammalian and plant cells in response to production of nitric oxide and reactive oxygen species. 8-Nitro-cGMP possesses signaling activity inherited from parental cGMP, including induction of vasorelaxation through activation of cGMP-dependent protein kinase. On the other hand, 8-nitro-cGMP mediates cellular signaling that is not observed for native cGMP, e.g., it behaves as an electrophile and reacts with protein sulfhydryls, which results in cGMP adduction to protein sulfhydryls (protein S-guanylation). Several proteins have been identified as targets for endogenous protein S-guanylation, including Kelch-like ECH-associated protein 1 (Keap1), H-Ras, and mitochondrial heat shock proteins. 8-Nitro-cGMP signaling via protein S-guanylation of those proteins may have evolved to convey adaptive cellular stress responses. 8-Nitro-cGMP may not undergo conventional cGMP metabolism because of its resistance to phosphodiesterases. Hydrogen sulfide has recently been identified as a potent regulator for metabolisms of electrophiles including 8-nitro-cGMP, through sulfhydration of electrophiles, e.g., leading to the formation of 8-SH-cGMP. Better understanding of the molecular basis for the formation, signaling functions, and metabolisms of 8-nitro-cGMP would be useful for the development of new diagnostic approaches and treatment of diseases related to oxidative stress and redox metabolisms.

Fluorescent probes for live cell imaging of endogenous Guanine nitration.

Seeing is believing: S-guanylation is a novel key mechanism by which signal transduction under oxidative stress is regulated. A chemical probe whose fluorescent intensity increases after the reaction with proteinous cysteine (S-guanylation) is described. The use of this probe revealed that S-guanylation products localized in lysosomes.